High-temperature corrosionresistant alloys



United States Patent ice 3,306,740 HIGH-TEMPERATURE CORROSION- RESISTANT ALLDYS Le Roy Wyman, Bethesda, Md., and John J. Park, Springfield, Va., assignors to the United States of America as represented by the Secretary of the Navy No Drawing. Filed Nov. 23, 1964, Ser. No. 413,379 1 Claim. (Cl. 75176) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to an improved nickelchromium base alloy having high resistance to corrosion at elevated temperatures in the presence of combustion products from fuels. More particularly the invention relates to alloys of the nickel-chromium base type having selected alloying elements added to improve their resistance to corrosion when used in ships boilers and where the alloy is subject to an environment containing compounds of vanadium, sodium, chlorine and sulphur.

It has been found that many alloys are attacked by such compounds as vanadium pentoxide to produce a relative low melting point mixture and thus cause the structure formed of the basic alloy to fail in a high temperature environment such as occurs in the fire-box of a ships boiler.

In the making of the present invention it was decided to produce an alloy which forms a surface layer resistant to fuel oil ash while retaining sufiicient ductility to permit the devices made from the alloy to be used without cracking or breaking.

It is an object of this invention to produce an alloy which is protected by a dense adherent coating which is non-slagging, self-healing and which serves as a diffusion barrier. In accomplishing this objective, one approach was to select alloying compounds from those which pro duce highly refractory oxide such as titanium and aluminum. Another approach was to select large-atom elements, such as the lanthanide metals i.e. misch-metal and yttrium.

In the preparation of these alloys it was found that for the most effective corrosion resistance the ingredients of the alloy must be of high purity and that they must be processed in a manner to maintain this degree of purity. Therefore, the basic ingredient, i.e. a binary alloy of 60% chromium, 40% nickel which ingredients are selected as commercially available high-purity electrolytic chromium and nickel. The additive elements were also selected as high-purity commercially available materials. By way of example, to avoid contamination in the processing, the ingredients were melted in magnesium crucibles and the meltwas ladled in-magnesium ladles. The melting was accomplished in an arg n atmosphere and an argon at- 3,306,740 Patented Feb. 28, 1967 mosphere was maintained during the pouring of the melt to the conventional baked-sand molds.

By test it was found that ternary alloys formed by adding to the /40 Cr/Ni alloy an alloying ingredient selected from the following table in a small but effective quantity from within the range indicated as percent by weight, produced improved resistance to corrosion from fuel oil-ash in oil fired ship-boilers.

TABLE I.ADDITIVES TO 60/40 Or/Ni BASE ALLOY Periodic Table Group Elements Peacenifilgy elg II {Calcium 0.04.

Magnesium 0.1 to 0.5. III. {Yttrium 0.1 to 1.0.

Rare Earths L-.. To 1.7. [V Titanium To 4% V Cnlnmhinm 0.04.

1 Lanthanides, Mischmetal.

The alloys produced from the additives listed in the foregoing table were specifically tested to determine their corrosion resistance to V 0 NaVO and NaSO and showed markedly improved resistance to corrosion when compared with the binary 60/40 Cr/Ni alloy, which Calcium 0.04%.

Magnesium 0.1 to about 0.5%.

Yttrium 0.1 to about 1.0%.

Rare earths A small but effective amount up to 1.7%. Titanium A small but effective amount up to 4%.

Columbium 0.04%

References Cited by the Examiner UNITED STATES PATENTS 2,809,139 10/1957 Bloom et a1 -176 X 2,955,937 10/1960 McGurty et al 75-1'76 3,015,559 1/1962 McGurty et al. 75176 3,235,380 2/1966 Scruggs 75-176 DAVID L. RECK, Primary Examiner.

CHARLES N. LOVELL, Examiner. 

